Styrene polymer foams by reason of their relatively low cost and low density are used in large volume as insulating and packaging materials. While such foams are widely used, it is recognized that they are subject to shortcomings which limit their use in certain applications. Such foams, particularly at low densities, have little physical strength and tend to be quite brittle.
In pending application Ser. No. 588,470, filed Mar. 12, 1984, the present applicant has disclosed that styrene polymer foams having higher softening points and lower melt viscosities can be prepared by extruding styrene-acrylic acid in admixture with sodium bicarbonate which functions as a foaming agent. The extrusion process converts the styrene-acrylic acid polymer to its sodium salt. While this styrene polymer foam is superior to styrene homopolymer foams for certain purposes, this novel foam is undesirably brittle. For this reason, it is difficult to continuously produce such a styrene polymer foam in sheet form by blown film extrusion processes.
For the above reasons, there is a need in the art for improved styrene polymer foams and economically attractive processes for preparing foamed sheet therefrom by blown film extrusion processes.